1. Field of the Invention
The present invention generally relates to water drainage systems and, more particularly, is concerned with an underground water drainage sump system and method of retrofitting the system for protecting a floor slab of a building. The present invention also is applicable to sub-slab depressurization for removal of polluting gases, such as radon, from a building.
2. Description of the Prior Art
The accumulation of water below the surface of the ground under a floor slab of a basement and around the foundation of a building can be a substantial problem in many areas of the country, particularly where the water table is high or rainfall is plentiful. For this reason, various approaches to finding a solution to this problem have been attempted in the past.
One widely-practiced approach has been to install a sump pump drainage system during the construction of the building. The process of installation of such system generally involves forming a sump hole in the ground before the floor slab is laid, placing a liner in the sump hole and then laying a porous water collection pipe along the foundation having its opposite ends extending into the sump hole through the liner for drainage of water therein from about the foundation. The floor slab is then poured over the pipe. Thereafter, a sump pump is placed in the sump hole for pumping the water collected therein into the sewer system where allowed or otherwise outside of the building away from the floor slab. Another approach taken during construction of the building, as proposed in U.S. Pat. No. 4,486,986 to Cosenza, involves providing for drainage of underground water from outside the building foundation through drain holes formed in the basement wall above the footing to a collection pipe laid around the inside of the foundation footing below the floor slab.
The solution to the problem of underground water accumulation is, of course, more difficult in the case of a building constructed without adequate provision of means for removing the underground water before it causes the foundation or basement floor to crack, buckle or flood. Various approaches to retrofitting the exterior of the foundation or interior of the basement floor of the building with some means for removing the underground water have been proposed in the prior art.
One approach to retrofitting a drainage means at the exterior of the building, as disclosed in U.S. Pat. No. 4,298,294 to Zimmerman, involves providing an exterior wet well at a location spaced from the building and extending to a depth below the lowest level of the foundation and placing a submersible pump therein which is operated to remove the water collected in the bottom of the well. Another approach to retrofitting a drainage means at the exterior of the building, as disclosed in U.S. Pat. No. 4,523,855 to DiFiore, involves providing an auxiliary drainage system in a trench which extends about the exterior of the foundation of the building. These exterior approaches have likely been found to be largely ineffective as solutions to the aforementioned problem in view that they do not appear to have been widely adopted because they are expensive and disruptive to the exterior landscaping.
One approach to retrofitting a drainage means at the interior of the building involves cutting a trench around the perimeter of the basement floor slab at its juncture with the foundation so that the underground water can then be collected and pumped from the building. However, this approach requires substantial alteration of the existing floor slab which may have unintended damaging consequences for the building and is expensive and disruptive to finished basements.
Various other approaches have proposed in the prior art to solving another problem involving the seepage of various gaseous pollutants, such as radon gas, from the underground soil into an existing building. Some representative examples of these approaches are disclosed in U.S. Pat. No. 4,858,521 to Heh, U.S. Pat. No. 4,905,579 to Dame, U.S. Pat. No. 4,938,124 to Garza, U.S. Pat. No. 4,949,626 to Townsend et al., U.S. Pat. No. 5,080,004 to Francis et al., U.S. Pat. No. 5,101,712 to Dean, Jr., U.S. Pat. No. 5,158,501 to Proskiw and in a U.S. Environmental Protection Agency publication entitled "Radon Reduction Techniques For Detached Houses-Technical Guidance" identified as EPA/625/5-86/019 and dated June 1986.
The approach disclosed in U.S. Pat. No. 4,858,521 to Heh involves retrofitting an exhaust system in the ground below and outside the foundation. In the approach of the Heh patent, a hydraulic press/impactor is utilized to drive sections of threaded and perforated pipe under a building footer and floor slab. A sufficient length of pipe is made by threading and bonding numerous such pipes together. Once the pipes are in place, each is then interconnected at one end to a plurality of above ground vent holes and at an opposite end to an above ground fan opposite the holes. When in operation, the fan creates a vacuum in the pipes causing the radon gas to be drawn out from the soil and into the pipes through the pipe perforations and exhausted to the outside air where it dissipates. While such retrofitted system may be effective for reducing the level of radon gas from soil in contact with points of entry into a building, it does not appear to be directly applicable to the problem of water accumulation below the surface of the ground under or around a foundation or basement.
Consequently, a need still remains for a suitable retrofitted underground water drainage system for protecting the floor slab of an existing building which does not adversely affect the structural integrity of the building floor slab and foundation and is minimally disruptive to the existing building.